"I firmly believe that the strong will, honest efforts and unique approach of myself and Your Excellency Mr. President aimed at opening up a new future between the DPRK and the US will surely come to fruition", Kim Jong Un said in the letter, dated July 6. "Great progress being made!"

North Korea has reportedly proposed holding general-level military talks with the United Nations Command (UNC) over the repatriation of remains of American troops killed during the 1950-53 Korean War, sources here said Thursday.

"I extend my conviction that the epochal progress in promoting the DPRK-US relations will bring our next meeting forward".

"I firmly believe that the strong will, honest efforts, and unique approach of myself and Your Excellency Mr. President aimed at opening up a new future between the DPRK [Democratic People's Republic of Korea] and the U.S. will surely come to fruition", the letter states, concluding, "I extend my conviction that the epochal progress in promoting the DPRK-U.S. relations will bring our next meeting forward".

Mr Pompeo had said progress was made during his two-day visit to Pyongyang. Pyongyang has asked the UN Command Armistice Commission to upgrade the talks to a higher level to include a US general, South Korea's foreign ministry said.

But it made no mention of any efforts by Pyongyang towards denuclearisation - a key issue the two leaders discussed at June's historic summit in Singapore.

North Korean officials have failed to turn up for talks with a United States team on the repatriation of the remains of American soldiers killed in the Korean war.

Representatives of the US and North Korea were expected to have working-level talks at the inter-Korean border truce village of Panmunjom on Thursday to hash out the details of the repatriation, but the discussions did not occur. The U.S. also risks giving the North Koreans leverage to continue diplomacy and drag out disarmament talks.

Representatives of the two countries had been poised to meet in Panmunjom, which is regarded as the truce village on the inter-Korean border.

Trump, on Thursday afternoon, tweeted out a letter he received from Kim Jong Un, along with a translated version.

The Defense Department estimates there are up to 5,300 sets of US service member remains still somewhere in North Korea.

There are about 7,700 U.S. soldiers classified as missing in action in the war.

"The US wanted to have talks as early as 12 July but the North did not seem to be ready", an unnamed Seoul official said.